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Fix gpio/dht_sensor #793

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Fix gpio/dht_sensor #793

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10 changes: 7 additions & 3 deletions gpio/dht_sensor/dht.c
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,8 @@

const uint DHT_PIN = 15;
const uint MAX_TIMINGS = 85;
// according to datasheet, 1 bit is 70us and 0 bit is about 26-28us
const uint BIT_THRESHOLD = 35;

typedef struct {
float humidity;
Expand Down Expand Up @@ -50,23 +52,25 @@ void read_from_dht(dht_reading *result) {
gpio_put(DHT_PIN, 0);
sleep_ms(20);
gpio_set_dir(DHT_PIN, GPIO_IN);
// stabilize, wait till the line actually rises
sleep_us(2);

#ifdef LED_PIN
gpio_put(LED_PIN, 1);
#endif
for (uint i = 0; i < MAX_TIMINGS; i++) {
for (uint i = 0; i < MAX_TIMINGS && j < 40; i++) {
uint count = 0;
while (gpio_get(DHT_PIN) == last) {
count++;
sleep_us(1);
if (count == 255) break;
}
last = gpio_get(DHT_PIN);
if (count == 255) break;
last = !last;

if ((i >= 4) && (i % 2 == 0)) {
data[j / 8] <<= 1;
if (count > 16) data[j / 8] |= 1;
if (count > BIT_THRESHOLD) data[j / 8] |= 1;
j++;
}
}
Expand Down
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